Design Brief: Problem Statement:

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Esther Dawson
6 years ago
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1 Design Brief: Problem Statement: The goal of this project is to design a safe, simple, and effective snowboard binding system for a triple amputee who lacks his right arm above the elbow and both legs above the knee. Special consideration was taken in providing safe damping because without knees, he cannot bend and absorb the impact force from riding a board. Our client s ability to attach to the snowboard while standing with ease can be done only using his left hand. These considerations will be used to fulfill the goal of keeping our client safe while snowboarding recreationally and potentially competitively. Background: Snowboarding is a winter sport which requires specific equipment with various design selections to cater to the snowboarder s needs. Boards vary depending on type of snow, rider s skill level, and the rider s personal preferences. Snowboard bindings attach to the board and hold the rider s boots in place. Bindings are selected based on the rider s skill level and flex level, or the range of foot motion needed when strapped in (REI, 2014). Common bindings include strap bindings and step-in bindings. Strap bindings, by far the most common, use two ratchet straps to secure boots in place at the ankle and toes (Nonstop, 2017). These bindings have multiple adjustment options and provide excellent support and cushioning. However, these bindings are cumbersome and require the rider to hunch over and use both hands to strap in while balancing oneself. Step-in bindings are less cumbersome and allow the rider to simply step on the binding and have rollers click onto the sides of the bottom of the boot. These bindings are very prone to clogging with snow, which makes it impossible to click in. A triple amputee will likely require a snowboard binding custom-designed to fit his needs. While past snowboarders with amputations have rode, each board and binding was predominantly designed for the intended rider. For example, Amy Purdy is a world-class snowboarder and a doubleabove-knee-amputee with a custom snowboard. This type of client-specific product creates a unique design challenge. Overall, when designing snowboard bindings, several factors need to be evaluated: 1) binding mounting mechanism, 2) binding fit to allow for a specific degree of flex, and 3) foot entry mechanism into binding (REI, 2014). This project depended on a significant amount of input from the customer to create a unique design to work for him. Approach: Customer input was the starting block for our design. Our client outlined three main tasks the design needed to include: 1) secure him to a binding while standing, 2) secure the

2 binding to the board, and 3) incorporate a damping system that reduces vertical impact without sacrificing control of the board. It also needed to be operable with one arm and limited range of motion in the legs. He did request that the system use a high-fill plastic 3D printed foot, made from a simplified scan of his current prosthetic feet, the College Park Sidekicks. This 3D printed foot would attach to the binding system directly, and it would be used instead of his Sidekicks in order to protect his everyday feet. Extensive external searches conducted for both existing products on the market and patented designs found designs unique to each individual, so these designs were unable to be transferred exactly to this project s needs. There are currently no snowboard bindings on the market geared for amputees. Instead, there are many prosthetic manufacturers who have designed complex prostheses that operate with standard snowboard bindings. Due to the nature of the team s prototype that is focused on a compatible binding instead of a new prosthetic limb, none of the existing products will be used. As a result, further research regarding individual shock absorbing components currently used in prosthetic technology was done. Various companies offer prosthetic feet designed to easily step in and go style to fit into normal ski bindings (Freedom Innovations, 2016). Another solution, is from BioAdapt, Inc., which has prosthetic attachments designed for high impact sports (US Patent 7,981,164 B1). We used features of previous designs and technology in order to brainstorm feasible new designs for our client through concept generation and ultimately selection of the best design. Methods: With these existing technologies and the customer needs in mind, the design process began with the basics to establish specifications. A forward-facing, or alpine, stance is being used for the design to allow our client maximum control of the board. A key to the design is a balance between damping and control. The board is controlled by small changes in weight distribution on the long edges of the board. A damping system needs to absorb as much impact as possible without absorbing all of the force used to control the board. To keep the rider close to the snowboard to keep his center of gravity low, and thus maximizing his control of the board, the binding and damping system must suspend him less than 5 inches above the board, a specification derived based on existing products (Freedom Innovations, 2016). To maximize the damping of the system in limited space on the board, the system will need to absorb approximately 5,000 in lbs per cycle, and the shock absorbers were selected based on their ability to absorb kinetic energy. This is based on our client s weight, approximately 130 lbs, and he will be experiencing a maximum vertical fall of 3 ft. With his weight being distributed evening between the damping systems, the assumption is that each shock absorber will need to absorb approximately 2,500 in lbs. In addition, all components of the system will need to be operable in cold temperatures as low as ~ 0 F.

3 Since our client has an end goal of competing in the Paralympics one day, The International Paralympics Committee (IPC) rule book was consulted. The rules that the IPC has in regards to bindings are that the bindings must be fixed diagonally on the long axis of the board. The boots cannot overlap each other. Plate systems that connect both bindings are not allowed. These regulations were used during the design process to ensure the design met the IPC s rules. To weigh the customer needs, an Analytic Hierarchy Process pairwise comparison was used, and the most critical customer needs were identified: safety, damping, and control. In order to ensure each of the customer needs were addressed by the engineering specifications, a Quality Function Deployment (QFD) approach was used to define customer needs and translate them to specific plans. Initially, each team member was assigned to independently come up with solutions and ideas based on these external searches and our discussion with our consultants. Four main designs were compared using the Pugh Concept Scoring Matrix, which allowed our team to make the design decision. Once the final design was selected (described in detail below), there was an alpha-prototype made of 3D-printed parts. The alpha prototype was assembled and used for simple testing, which then allowed for modifications and redefining the design before advanced prototyping. Description of Final Approach and Design This project involves the design and construction of the following components: 1) a highfill plastic foot that can attach to the end of the prosthetic legs that our client currently uses, 2) a new type of binding which will fit around client s feet and allow him to stand, 3) damping system to reduce stress on his hips, and 4) base plate into which the bindings will be fitted to attach to the snowboard. The selected design had many components. The base was designed to align with the resting position of our client s feet, and connected to the snowboard via a series of holes drilled at its bottom. The damping system is bolted to the upper surface. The damping system was designed to absorb sudden impacts, which would typically be handled by a knee. Figure 1 shows the damping system; features include a shock absorber (1) at its rear end with an adapter piston (2) that is able to move axially. The piston is connected to a foot plate (3), where the clamp for our client s prosthesis will be bolted, via a travel arm (4) that is constrained by two sets of rails (5). As an impact occurs, the shock absorber will provide resistance against the compression of the foot plate, reducing the force on our client s body. Figure 1 shows the position of the damping system while being compressed by our client s weight. Figure 2 illustrates its response to an impact. The foot plate compresses, causing the travel arm to slide along its rails and compress the shock absorber. The shock absorber resists the motion of the travel arm, reducing the force felt by our client.

Figure 1: Snowboard binding design in the neutral position.

Finally, the foot clamp system was designed to secure the current prosthetic foot

the easiest way for him to step in. He also needed to use it with one hand.

system, and a swinging clamp (7) that locks the foot (8) into the base securely with

4 Figure 1: Snowboard binding design in the neutral position. Figure 2: Snowboard binding in the compressed position. Finally, the foot clamp system was designed to secure the current prosthetic foot into the damping system, and our client thought that swinging in sideways would be the easiest way for him to step in. He also needed to use it with one hand. It features two pieces, a base (6) that is bolted to the foot plate of the damping system, and a swinging clamp (7) that locks the foot (8) into the base securely with a single pin. Figure 3 shows the foot clamp system in its open position and closed position. Figure 3: Mounted foot clamp system in the open and closed position.

5 Material Selection for Prototype: Aluminum 6061 (A1 6061) was chosen, over stainless steel, to construct the footplate, travel arm, baseplate, due to its durability in in-climate weather, lighter weight, lower cost, and ease of manufacturing. Lighter weight was especially beneficial since the less weight on the board correlates to more control in shifting the board. Regarding the smaller components (pins and shock mounting bracket) of the system, stainless steel was used because these units will be under higher stress and should not fail under loading. The shock absorber portion of the damping system will support our client s weight and distribute kinetic energy due to vertical impact. Two shock absorbers, which are Ace Control s TS profile dampers, have been purchased from Rankin Automation. These barrel shaped elastomer shock absorbers fit the dimensions of the system, operate at sub-zero temperatures, are resistant to water and chemicals, and are very affordable. To account for the necessary kinetic energy absorption of 2,500 in-lb in each shock absorber, TS profile dampers were selected for their ability to absorb 2,600 in-lb. The components for the rail system were purchased from McMaster Carr and attach to the travel arm of the damping system via two adapters attached to rolling bearings. Outcome: Initially, the 3D model in CAD was analyzed with the calculated loads to assess stresses and strains on the design, but appropriated testing will need to be done on the prototype. Both the 3D printed model and the final prototype must be tested. Initially, the alpha-prototype, which was constructed with 3D-printed components printed with low-fill plastic, was used as a full-size model to show how the pieces will fit together. This model was used with our client to inspect the angle of the binding base, the distance between the two bindings, the damping system, as well as if our client can use it with one hand. Additional testing needs to be done to analyze the stresses on each component of the binding, especially the high stress parts like pins and thinner plates. This prototype allows for testing and evaluation of design flaws, so the team can make adjustments and changes before more advanced prototyping. Once the final prototype is complete with the finalized materials, we will meet with our client again to perform the same tests done with the alpha-prototype. While the ski slopes are closed currently, and our client cannot ride on the snow, the bindings can be tested. By strapping his feet into the binding, he can rotate and determine his level of comfort. Our client can also practice jumping lightly in-place with the bindings to test the effects and see how the damping system feels to him. Finally, the bindings will be attached to our client s snowboard and repeat the same tests: shifting to find comfort in the stance, test jumping in-place, and practicing motions of snowboarding. No outside equipment will be needed for these types of tests, except for a person or sturdy surface to hold onto in case of a fall. Outcomes will be measured based on these preliminary tests, our client s satisfaction, and further testing once the weather permits. The client s satisfaction will be measured based

6 on a questionnaire with the following open ended questions: Is the angle of the wedges what you expected? Should they have been higher, lower, or more inward or outward facing? Is the amount of damping what you had expected or would you have preferred more or less? Do these bindings, when placed on the board, provide you with a comfortable stance? Overall, do you think this board will satisfy your needs and provide a safe and fun snowboarding experience? Overall, the testing will demonstrate if the product met the requirements of being a safe, simple, and effective snowboard binding system that our client is happy with. Cost: Our design incorporates materials from outside vendors as well as our own original design. The raw cost of the materials is approximately $ To breakdown, 2 profile dampers cost $60, track and bearings system $450, raw aluminum sheets $93, and pins/screws $50. Parts were either purchased or machined by our team. Our design was customized to our client and his specific prosthetic attachments he wished to attach to the snowboard. For replication and further manufacturing of our product, our team could customize and modify the CAD model and 3D print a client-specific model. This would require more time and re-design, which would alter the price of the device. With this client-specific product, prices could range from $ depending on the amount of modifications. Significance Our team was able to design a client-specific safe snowboard binding. It was our goal to work with our client to help develop a way for him to resume one of his favorite hobbies. We wanted to help design something that could give him the chance to regain a part of his life. Our current product is designed specifically for our client, but the future of our product lies in the customizability. With our product including some standardized parts, the CAD model could be altered to fit the requirements of each client and then 3D printed and manufactured. Our product includes dynamic features which allows for easy customizability, which opens up possibilities of helping future clients to achieve their goals of safe snowboarding. With the innovation and technology used to create modified devices for sports and hobbies, the impossible is starting to become the possible for these clients. And we hope that our product too will make these dreams into a reality.

7 Acknowledgements: Throughout the design process, our team was supervised by Dr. Everett Hills and Victoria Heasley from Penn State College of Medicine. Our client was Zach Sherman, who provided excellent insight and description of what he needed. It was also in collaboration with Central PA SCI Support Group. It is important to credit several collaborators who have worked to help our client in his snowboarding endeavor. Aaron Wilson of Funtastik Skate and Snow contributed his knowledge of snowboarding and inspired a mechanical suspension idea and helped to sketch an initial design. Consultant Bryan Palleschi worked with our client for several months to develop a 3D printed model of the Sidekick foot that our client plans to attach to his prosthetic in the future. He explained the extensive research and prototyping of our client s 3D printed feet and answered a lot of our team s questions. Reference: "Biodapt, Inc." From Biodapt, Inc. N.p., n.d. Web. 10 Feb "Flow vs Ratchet Snowboard Bindings." Nonstop. N.p., n.d. Web. 10 Feb "Slalom Ski Foot." Freedom Innovations. N.p., 02 Dec Web. 27 Jan < "Snowboards: How to Choose." REI. N.p., 02 Dec Web. 10 Feb "Snowboard Bindings: How to Choose." REI. N.p., 03 Dec Web. 10 Feb <

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